1. Field of the Invention
The present invention relates to a control apparatus for an optical density changing element including an electrochoromic material, which changes an optical density utilizing an electromotive force according to an intensity of an electromagnetic wave.
2. Description of the Related Art
A element showing a change in an optical density in response to an electromagnetic wave has a wide field of application. As a material having a function of changing the optical density, namely controlling a light transmission or a light reflection in response to an electromagnetic wave, there are known a photochromic material and an electrochromic material.
The photochromic material is a material capable of changing an optical density thereof in response to a light irradiation, and is applied to sunglasses, an ultraviolet checker, printing-related materials, processed fiber products and the like.
The electrochromic material is a material capable of changing an optical density thereof in response to an electron injection or an electron emission, and is applied to an antiglare mirror for automotives, an automotive window material and the like.
The application of such optical density changing material includes a photographing system, including a camera. For example, a film with lens is recently popular, because of its simplicity in operation, as a camera unit not requiring a film loading operation and enabling a photographing operation immediately after purchase. Also a high sensitivity film is being loaded in order to elevate the value of utilization. However the related film with lens is not provided with a mechanism for regulating an exposure amount, as it is designed for simplicity. Therefore, a film with lens, loaded with a high sensitivity film, results in an overexposure in a photographing operation in a bright environment, thus often generating a failed whitish picture. Therefore, a film with lens capable of automatic switching of a diaphragm according to the light amount at the photographing, utilizing an AE control by a light metering in the photographing operation, has been commercialized. This has significantly reduced the photographing failure caused by the excessive exposure amount.
For realizing a “light regulating filter” for regulating the incident light amount to a photosensitive material, according to the light amount at the photographing operation, in a simple and inexpensive manner, there is proposed a film with lens utilizing the aforementioned photochromic material (for example JP-A No. 5-142700, JP-A No. 6-317815, JP-A No. 11-352642 and JP-A No. 2001-13301). More specifically, a photochromic material means a material having a property for generating a color or increasing an optical density when subjected to a light irradiation of a certain wavelength, and extinguishing the color or decreasing the optical density when the light irradiation is terminated or when subjected to a heating or a light irradiation of a different wavelength, and such property is known in inorganic compounds containing silver halide and in a part of organic compounds. A light regulation is considered possible by positioning a filter, formed by a photochromic material, on an optical axis and executing color generation and color erasing according to the incident light amount.
However, the photochromic compound generally requires about 1 minute for the color generation and about several tens of minutes for color erasing (cf. Solid State and Material Science, 1990, Vol. 16, p. 291), and is therefore difficult to employ as a light regulating system for a photographing light.
On the other hand, the aforementioned electrochromic material is known to be capable of faster color generation and color erasing. More specifically, the electrochromic material means a material having a property of increasing an optical density by an electron injection or an electron ejection under a voltage application, and decreasing the optical density by an electron transfer opposite to that at the increase of the optical density, and such property is known in certain metal oxides and organic compounds.
A light regulating system, laminating a solar cell generating an electromotive force in response to a light with an electrochromic material, is proposed (for example JP-A No. 9-244072). An automatic light regulation according to the light can be expected also in this system. However, in such proposed structure where the solar cell and the electrochromic material are superposed, a part of the light passing through the electrochromic material is inevitably absorbed by the solar cell, and such structure is therefore unsuitable for a system of a camera-related optical element in which it is desired to utilize the incident light amount to the photographic recording medium as maximum as possible in a scene not requiring such light regulation.